Sorry - I just re-read your message and it sounds like your friend has just received the PR visa now but has not landed in Canada. If that's the case, should notify the visa office immediately that he now has a wife and children. He should then return the visa he has now and submit the paperwork required to add his wife and children to his application. The visa office will then process their forms and re-issue a visa for him and his entire family once this additional processing has been completed.
Tell him that he cannot use the visa he has now to land (if he uses it to land, he will never be able to sponsor his wife and children and could have his own PR status revoked for lying about his status on landing).